1. Field of the Invention
This invention relates to a seat that has a front surface of the seatback (i.e., seat surface of the seatback) that can contact the occupant's back at a large area.
2. Description of the Related Art
Any seat should be make the occupant feel well fit in it when seated on it. A vehicle seat, for example, must be so designed that the occupant may feel well fit in it, thus reducing his or her fatigue resulting from a long sitting in the same posture. The fatigue is reduced by, for example, increasing the contact area at which the occupant's back contacts the seat surface of the seatback, thus making the occupant feel well fit in the seat.
A seat having an increased contact area is known. The seat has two ridge-shaped bulging parts called “side supports,” at the left and right edges of the seatback. The side supports cover the left and right sides of the occupant, respectively. In most cases, the side supports are formed integral with the seatback. Therefore, they may or may not support the occupant well, depending on the occupant's physique (particularly, trunk width). If the occupant is of the average physique (having the average trunk width), the side supports hold him or her, as if wrapping the sides from the left and right, respectively. As a result, the occupant's back contacts the seat surface of the seatback, at a large area and at an appropriate pressure, making the occupant feel well fit in the seat.
If the occupant is a small person (i.e., slender person with a narrow trunk), however, there will be gaps, each between either side of the occupant and the side support facing the side. Due to the gaps, the side supports fail to support the occupant at the left side or the right side. Consequently, no sufficient contact area is provided between at the occupant's back and the seat surface, and the occupant cannot feel well fit in the seat. If the occupant is a big person (i.e., fatty person with a broad trunk), his or her back will push the side supports, as if collapsing the side supports. In this case, the contact pressure is high, making the occupant feel something strange. As a result, the occupant cannot feel well fit in the seat.
Most seatbacks are formed substantially flat. This is why the occupant's back, particularly the shoulder blades, is greatly pushed to the seat surface of the seatback in most cases. The contact pressure is therefore high at that part of the seatback, which contacts the shoulder blades, and the contact area is small. As a consequence, the occupant cannot feel well fit in the seat.
In the seat disclosed in JP 2011-084207A, for example, the wadding (i.e., elastic layer) interposed between the pad and trim cover of the seatback is thicker at the inner part than at outer parts that contact the side supports. The wadding may therefore cushion the occupant more at the inner side of either side support than at the outer side thereof. The thick inner part of the wadding, which lies between the side supports, undergoes elastic deformation. This makes the occupant feel well fit in the seat.
JP 01-147131U (JP 05-034430Y) discloses a seat so designed that the seat surface of the seatback may well support the occupant's shoulder blades. The pad of this seat incorporates two air mats, respectively at the left and right parts the seat surface of the seatback, which support the shoulder blades. If the occupant's shoulder blades push the seat surface of the seatback, the air mats will be deformed, and the seat surface of the seatback will softly support the shoulder blades. Therefore, the shoulder blades would not be strongly pushed to the seat surface of the seatback, and the air mats is well deformed. As the air mats are deformed, the seat surface of the seatback goes into close contact with the occupant's shoulder blades, providing a large contacting area. Thus, the seat surface of the seatback can support the occupant's back, making him or her feel well fit in the seat. The left and right side supports are not disclosed in the drawings.
If the cushion of the inner side of either support provided on the seat surface of the seatback is enough large and the wadding of the inner side of either side support is enough broad, a large contact area can be provided without increasing the contact pressure, no matter whether the occupant is small or big. The occupant can therefore feel well fit in the seat. If the wadding is thick and broad inside the side supports, however, the seat surface of the seatback may be impaired in outer appearance. Further, the seatback will inevitably become complex in structure, because the side supports are arranged on the seat surface and also because the wadding has a different thickness between the inner and outer side supports.
As described above, the air mats are deformed, supporting the occupant's shoulder blades. The air mats must therefore be incorporated in those parts of the pad, which exist at the left and right sides of the seat surface of the seatback. Inevitably, the seatback becomes complicated in structure.
An object of this invention is to provide a seat which provides a large contact area without complicating the structure of the seatback, making the occupant feel well fit in the seat.